Question: The lifespans of lizards in a particular zoo are normally distributed. The average lizard lives $3.3$ years; the standard deviation is $0.8$ years. Use the empirical rule (68-95-99.7%) to estimate the probability of a lizard living between $2.5$ and $4.9$ years.
Answer: $3.3$ $2.5$ $4.1$ $1.7$ $4.9$ $0.9$ $5.7$ $95\%$ $68\%$ $13.5\%$ $13.5\%$ We know the lifespans are normally distributed with an average lifespan of $3.3$ years. We know the standard deviation is $0.8$ years, so one standard deviation below the mean is $2.5$ years and one standard deviation above the mean is $4.1$ years. Two standard deviations below the mean is $1.7$ years and two standard deviations above the mean is $4.9$ years. Three standard deviations below the mean is $0.9$ years and three standard deviations above the mean is $5.7$ years. We are interested in the probability of a lizard living between $2.5$ and $4.9$ years. The empirical rule (or the 68-95-99.7 rule) tells us that $95\%$ of the lizards will have lifespans within 2 standard deviations of the average lifespan. It also tells us that $68\%$ of the lizards will have lifespans within 1 standard deviation of the mean. The probability of a particular lizard living between $2.5$ and $4.9$ years is ${68\%} + \color{orange}{13.5\%}$, or $81.5\%$.